1. Field of the Invention
This invention relates to cobalt (II) thiobis (alkylphenolates) as novel compounds and to organic compositions, such as lubricants and plastics, normally subject to oxidative degradation, containing a minor amount of said cobalt phenolates, sufficient to impart antioxidant characteristics thereto. This invention further relates to synergistic and improved antioxidant combinations of the cobalt thiobis phenolates in accordance herewith and certain aryl amines and/or hindered phenols. Additionally, this invention relates to organic compositions wherein a minor amount of said novel cobalt (II) thiobis(alkylphenolates) provides effective energy quenching stabilization and antisludging properties.
In a more particular aspect this invention is directed to the above referred to novel cobalt (II) thiobis phenolates and lubricant compositions containing them, which lubricant compositions include oils of lubricating viscosity, hydrocracked lubricating oils, hydraulic oils, mineral oils or fractions thereof, automotive oils, gear oils, transmission fluids, waxes, greases and other forms, natural or synthetic, of lubricants normally requiring the presence of stabilizing agents against oxidative degradation. Contrary to expectations, the subject cobalt (II) thiobis(alkylphenolates) when complexed with certain arylamines, also function well as oxidation inhibitors, i.e. antioxidants, ultraviolet stabilizers and energy quencher stabilizers.
2. Description of the Prior Art
In general, the production of lubricant compositions, for example, lubricating oils produced by hydrocracking, affords a relatively high viscosity index and permits the use of certain stocks that would be unsuitable for other processes. On the other hand, however, hydrocracked lubricating oils tend toward poor stability against ultraviolet light degradation, rapidly forming suspended and/or precipitated insoluble material on exposure to ultraviolet light, such as sunlight, or other sources of actinic radiation. Compounds capable of absorbing ultraviolet light, for example, hydroxybenzophenones, and hydroxyphenyl benzotriazoles, have afforded some improvement in the light stability of hydrocracked oils. Conventional antioxidants have also provided some benefit.
In the literature, Heskins and Guillet in "Mechanism of Ultraviolet Stabilization of Polymers", Macromolecules 1, 97 (1968) first proposed the energy transfer mechanism of ultraviolet protection. Commercially available ultraviolet stabilizers are also listed by class and function and identified as to structure in the Kirk-Othmer Encyclopedia in "Encyclopedia of Chemical Technology", Second Edition, Vol. 21, pp. 115-122. Uri in "Thermal and Photochemical Oxidation of Polymers and Its Prevention", Chemistry and Industry, Mar. 1, 1975, pp. 199-203, cites conventional antioxidant effects (hydroperoxide decomposition and free radical capture) of bis(stilbenedithiolato)nickel and its ultraviolet inhibiting properties. In British Patent specification No. 1,263,910 (1972), there is disclosed bis(stilbenedithiolato)nickel as an antioxidant for plastic materials. The compounds being useful in lube oils and functional fluids. Further, U.S. Pat. Nos. 2,703,786, 2,716,090 and 3,210,277 disclose the use of polyvalent metal (e.g. Ni) salts of alkyl phenol sulfides as oxidation inhibitors and plasticizing agents. Various polyvalent metal (e.g. nickel) compounds are disclosed in the patent literature, for example, U.S. Pat. No. 3,630,897 discloses metal salts (e.g. nickel, iron, zinc) of substituted dithiocarbamic acids and U.S. Pat. No. 3,252,910 discloses compounds such as nickel N,N-substituted dithiooxamides. U.S. Pat. Nos. 2,971,940 and 2,971,941 disclose nickel phenol-phenolate complexes as being useful in stabilizing polyethylene and polypropylene.
None of the foregoing disclosures, however, show organic, e.g., lubricant compositions containing the organo sulfur-containing cobalt (II) complexes described in accordance with this invention.